The invention relates to a blood treatment apparatus, and particularly to a blood treatment apparatus provided with a device for on-line preparation of a treatment liquid.
Specifically, though not exclusively the invention can be usefully applied in a dialysis machine provided with a device for preparing on-line a dialysis liquid from water and concentrates.
As is well known, air bubbles in the dialysis liquid render inoperative the semipermeable membrane of the dialyzer. Therefore a dialysis machine normally includes a device for removing gas and minimizing gas in the dialysis liquid. For example, one type of gas removal system, as shown in U.S. Pat. No. 3,738,382, includes a heater for heating the water to a high temperature and a debubbling chamber for removing gas from the heated water at atmospheric pressure. This system does not effectively degass the water and the heating of the water causes dissolved minerals to precipitate and clog passageways within the dialysis machine. A second type of gas removal system is shown in U.S. Pat. No. 3,528,550. In this system water is fed to a degassing chamber which is maintained at a pressure below atmospheric pressure by a Venturi through which dialysis solution flows. Thus the pressure in the degassing chamber is directly related to the dialysis solution flow rate through the Venturi. The Venturi only applies a moderately negative pressure to the degassing tank and thus does not effectively degass the water. In the degassing system shown in U.S. Pat. No. 3,528,550, the degassing chamber pressure may vary with dialysis solution flow rate, which, in turn, may vary with dialysis conditions, such as patient size, etc. Variations in degassing chamber pressure may affect gas removal. During dialysis it is desirable to control the dialysis solution pressure in the dialyzer. However, changes in the dialysis solution flow rate through the dialyzer cause the dialysis solution pressure to vary.
U.S. Pat. No. 4,348,280 provides a degassing system which functions independently of the dialysis solution flow rates and further provides means for controlling the dialysis solution pressure in the dialyzer as the dialysis solution flow rate changes. In the degassing system proposed by U.S. Pat. No. 4,348,280 water at normal body temperature is fed to a degassing tank that is continuously subjected to a controllable high negative pressure. The pressure is provided by two pumps, one of which draws gas from the tank and another of which draws degassed water from the tank. The degassing tank pressure is thus independent of the dialysis solution flow rate. The dialysis solution pressure and flow rate at the dialyzer are controlled by a pair of flow restrictions which are positioned one upstream and the other downstream of the dialyzer. This permits accurate control of the dialysis solution flow rate and pressure within the dialyzer.
U.S. Pat. No. 4,153,554 discloses an apparatus for delivering a dialysate solution to an artificial kidney. The apparatus prepares the solution by mixing water with a concentrated solution in a predefined ratio. The water enters a heater and then flows into a float tank which is filled with a controlled volume of water by means of a float-controlled valve. Air bubbles are removed from the tank by means of a vacuum pump, which creates a partial vacuum on the float tank and passes air out of a vent. The water is then drawn from the float tank by a supply pump and boosted back to about +5 psig pressure which is maintained by a pressure regulator arranged downstream to the supply pump. A deaerator removes additional air from the water by passing the water over a vertical baffle near an upper air space which is in communication with the top of the float tank by means of a line having a restriction which is adapted to maintain the 5 psig pressure in the deaerator and thus in the water as it leaves the deaerator. Since the supply pump has a constant pressure of about 5 psig to work against, it is possible to maintain a steady flow of dialysate out to an artificial kidney.
The hemodialysis apparatus of U.S. Pat. No. 4,828,693 comprises means for removing air entrapped in the incoming water from the water stream prior to a proportioning pump. The air is removed in a deaeration loop utilizing a deaerator having a float valve and air outlet. The incoming water is fed to a deaerator pressure regulator having an outlet to the deaerator. The deaerator outlet is connected to a pump, thence back to the pressure regulator completing the deaeration loop. The pump creates a negative pressure in the deaerator pressure regulator, drawing the incoming water into the deaerator at which point the entrapped air in the water escapes via the float valve and air outlet at a lower negative pressure. The deaeration pressure regulator controls the negative pressure to a selected value, for example −23 inches of mercury. The incoming water to the deaeration pressure regulator is generally controlled by a first pressure regulator to 12 psig. The outlet water from the deaeration pressure regulator is supplied to the proportioning pump. U.S. Pat. No. 4,828,693 adds a second regulator, termed a back pressure regulator, to receive water from the deaeration pump and to control the pressure of that water to a value higher than 12 psig; for example, 15 psig. The output from the backpressure regulator then supplies the water to the dialysate-proportioning pump. Thus, the pressure of the water to the proportioning pump is independent of the incoming water pressure since the deaerator loop serves as a constant volume source of water to the pump and the pump is independent of the incoming water pressure and flow.
U.S. Pat. No. 4,229,299 describes a dialysate proportioning system provided with deaeration means for removing soluble gases from the heated water prior to passage thereof to the proportioning means. Water containing desolubilized gases is passed from a heater to a first vented tank. Partially deaerated water is removed from the first tank through a conduit into a second vented tank. The conduit has an adjustable flow restrictor which depressurizes the liquid so as to release additional soluble gases therefrom. A pressure sensor is arranged downstream from the restrictor to permit any necessary adjustment of flow restrictor in order to maintain a predetermined pressure level. A vacuum pump is arranged on the conduit downstream from the pressure sensor. In order to enhance removal of soluble gases, a recirculation conduit joins the first tank with the second tank for recirculation of a portion of the finally deaerated water from the second tank to the first tank.
U.S. Pat. No. 5,762,782 describes a water treatment process for use in a dialysate preparation machine wherein warm water is passed through a water pressure regulator past a manually operated valve. The pressure regulator supplies water to the dialysate preparation unit at a substantially constant pressure. The water then passes through a chamber loaded with a carbon filtration agent which removes organic material and dissolved gases from the water.
WO 00/57935 describes an apparatus for the preparation of peritoneal dialysis fluid wherein preheated water passes through a series of components which remove dissolved gas from the water. These components are a proportioning valve, a degassing restrictor, an expansion chamber, a degassing pump and a degassing chamber. In operation, water from the degassing chamber is recirculated via the proportioning valve through the degassing restrictor by the degassing pump. The pressure drop in the water due to the degassing restrictor causes dissolved gas in the water to be forced out of solution and begin to form bubbles in the water. The pressure drop due to the degassing restrictor is a function of the flow rate there-through, which is maintained constant by recirculation from the degassing chamber, at a flow rate set by the degassing pump.
The prior art includes also AK 100/200/95® dialysis machines (produced by Gambro®) each of which comprises a blood treatment apparatus as in the preamble of claim 1.